The present invention generally concerns an improved differential drive, and more particularly relates to a positive traction differential unit using drive balls for differentially transferring rotational forces from a central member to drivable shafts on either side of the central member.
Differential transmission units, generally for allowing a common rotational input to be differentially transferred between two axle shafts, have long been in existence. For example, in one type of differential transmission unit such as sometimes used in a rear wheel drive automobile, when either of the rear driving wheels begin to slip due to loss of traction, driving input from the automobile drive shaft is diverted to that wheel, and the power to effectively move the vehicle is thus in proportion to the traction of the slipping wheel.
In some cases, power delivered from the drive shaft to the non-spinning wheel is insufficient to move the vehicle, because substantially all of the driving power is being diverted to the slipping wheel. In such an event, the vehicle may become immobilized due to the lack of traction of the spinning wheel (even though the non-slipping wheel may have sufficient traction). Because substantially all of the driving power from the drive shaft is transferred to the slipping wheel by the differential unit, the non-slipping wheel never receives sufficient rotational input for mobilizing the vehicle.
Other types of differential transmission units may be locked manually or automatically for transmitting rotational drive power from a drive shaft to a pair of drive axles so that wheels mounted thereon deliver driving torque to a road surface, even if one of the wheels tends to slip or spin. Such differential transmission units are commonly referred to as limited slip or positive traction differential units. Unit locking may be variously accomplished. For example, U.S. Pat. No. 2,967,438, granted to Altmann, and U.S. Pat. No. 2,938,407, granted to Nallinger et al., each prevent a slipping wheel from receiving all of the driving input from a driving shaft, by diverting some power from the driving shaft to the axle connected to the other (non-slipping) wheel. The Altmann and Nallinger units have balls which selectively engage different members during operation.
Other known differential transmission units use movable balls, such as disclosed in U.S. Pat. Nos. 3,130,604 (Johnson et al.); 2,841,036 (Decker); 1,823,092 (granted to De Lavaud); 1,282,614 (Miller); and 1,238,659 (Ford).
U.S. Pat. No. 1,162,754, granted to Deegan, discloses another exemplary differential unit, and uses sliding members ("dogs") disposed within a driving ring which engage and drive follower plates carried adjacent the driving ring. The follower plates are in turn each connected to respective drive shafts for rotation therewith.